1. Field of the Invention
The present invention generally relates to a plasma CVD apparatus used in a semiconductor manufacturing process; particularly to a shape of a shower plate provided in the plasma CVD apparatus.
2. Description of the Related Art
A conventional plasma CVD apparatus possesses a first and a second electrodes disposed parallel to each other inside a vacuum chamber; the first electrode has a hollow structure for introducing source gases into the vacuum chamber and has a shower plate removably attached in its bottom face; in the shower plate, many gas inlet holes are formed.
A conventional shower plate is disk-shaped and has many gas inlet holes of a given diameter being formed with an arrangement to be adapted to pass completely through to the reverse face of the shower plate from its front face.
Additionally, as shown in FIGS. 15(a) and (b), there is a shower plate having gas inlet holes having diameters gradually increasing to the direction of gas flow (for example, see U.S. Pat. No. 4,854,263). This shower plate has larger apertures on its forefront surface in a honeycomb-shaped surface pattern as shown in FIG. 16.
Conventional plasma CVD apparatuses have a problem in that it is difficult to form a thin film having desired properties stably with excellent controllability or reproducibility. That is, the operable ranges to produce desired films are narrow. This problem cannot be solved even by using the shower plate of U.S. Pat. No. 4,854,263.
Additionally, the shower plate of U.S. Pat. No. 4,854,263 has another problem in that its shape pattern gets to be transferred to a film thickness distribution of a thin film formed.